perf/x86: Introduce a ->read() callback in 'struct x86_pmu'

Auto-reload needs to be specially handled when reading event counts.
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Link: http://lkml.kernel.org/r/1518474035-21006-3-git-send-email-kan.liang@linux.intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/core.c

@@ -1881,6 +1881,8 @@ early_initcall(init_hw_perf_events);
 
 static inline void x86_pmu_read(struct perf_event *event)
 {
+	if (x86_pmu.read)
+		return x86_pmu.read(event);
 	x86_perf_event_update(event);
 }
 

arch/x86/events/perf_event.h

@@ -520,6 +520,7 @@ struct x86_pmu {
 	void		(*disable)(struct perf_event *);
 	void		(*add)(struct perf_event *);
 	void		(*del)(struct perf_event *);
+	void		(*read)(struct perf_event *event);
 	int		(*hw_config)(struct perf_event *event);
 	int		(*schedule_events)(struct cpu_hw_events *cpuc, int n, int *assign);
 	unsigned	eventsel;